1. Field of the Invention
This invention relates to thermoplastic elastomers based on engineering thermoplastics, and which have improved high temperature performance while retaining excellent elongation characteristics. A thermoplastic elastomer is generally defined as a polymer or blend of polymers that can be processed and recycled in the same way as a conventional thermoplastic material, yet has properties and performance similar to that of vulcanized rubber at service temperatures. Blends or alloys of plastic and elastomeric rubber have become increasingly important in the production of high performance thermoplastic elastomers, particularly for the replacement of thermoset rubber in various applications.
2. Description of the Related Art
Polymer blends which have a combination of both thermoplastic and elastic properties are generally obtained by combining a thermoplastic with an elastomeric composition in a way such that the elastomer is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with vulcanized compositions is found in U.S. Pat. No. 3,037,954 which discloses static vulcanization as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the polymer blend. The resulting composition is a micro-gel dispersion of cured elastomer, such as butyl rubber, chlorinated butyl rubber, polybutadiene or polyisobutene in an uncured matrix of thermoplastic polymer such as polypropylene.
U.S. Pat. No. 5,003,003 is directed to blends of polyamide resin with elastomeric ethylene-propylene polymers which have been functionalized, then crosslinked after dispersion in the polyamide resin. The resulting blend has improved tensile strength, elongation and oil resistance.
PCT Published Application WO 92/02582 describes blends of thermoplastic engineering resin with an elastomeric halogen-containing copolymer of a C.sub.4-7 isomonoolefin and a para-alkylstyrene. The elastomer component of the blend may be cured or uncured.
U.S. Pat. No. 5,238,990 discloses a thermoplastic blend of polyamide with a grafted polymer which is a reaction product of (a) a copolymer or halogen-containing copolymer of a C.sub.4-7 isomonoolefin and an alkylstyrene, and (b) an unsaturated carboxylic acid or a derivative thereof. The blend is said to have improved impact strength while maintaining the high flexural modulus of the polyamide.
In U.S. Pat. No. 5,244,961, a process is described for the preparation of a blend of thermoplastic polyamide and halogen-containing copolymer of C.sub.4-7 isomonoolefin and paraalkylstyrene, in the presence of a metal compound. The blend has improved impact resistance at low temperatures.